Updated October 6, 2026
Quick answer: Flu season in Southern California usually builds in late fall and peaks between December and February. Get your 2026-2027 flu shot in September or October if you can, since it takes about two weeks to protect you, and come in within 48 hours of sudden flu symptoms, when antiviral medicine works best.
Walk in for your flu shot, no appointment needed, at 797 S Arroyo Pkwy, Pasadena. We are open Monday to Friday 8:00 AM to 8:00 PM and Saturday and Sunday 9:00 AM to 5:00 PM, and we take our last patient 30 minutes before close.
What is new for the 2026-2027 season
All three virus components of this season's U.S. flu vaccines were updated, in part because an influenza A (H3N2) subclade spread widely last season. Every flu vaccine for 2026-2027 is trivalent, protecting against one H1N1, one H3N2, and one B/Victoria virus. Adults 65 and older are advised to get a high-dose, recombinant, or adjuvanted flu vaccine when one is available, and people with an egg allergy can receive any flu vaccine that is otherwise right for their age and health. As of the CDC report for the week ending September 26, 2026, flu activity in the United States was low but increasing. Our flu symptoms guide tracks where the season stands.
The flu shot: timing beats perfection
September and October are the sweet spot: early enough to be protected before activity rises, and late enough that protection lasts through the peak. It takes about two weeks after the shot for immunity to build. Getting vaccinated later in the season is still worthwhile, since some protection always beats none. The CDC recommends a yearly flu vaccine for everyone 6 months and older without a reason to avoid it, and it matters most for young children, adults 65 and older, pregnant patients, and anyone with asthma, diabetes, or heart disease. Wondering how you will feel afterward? Our flu shot side effects guide covers what is normal and what is not.
Flu, cold, or COVID? How to tell
The flu announces itself: sudden fever, body aches, chills, exhaustion, headache, and cough, often within hours. Colds build gradually and stay mostly in the nose and throat (our strep vs. flu guide covers the sore throat question). COVID-19 overlaps with both. Symptoms alone cannot reliably separate them, but a quick swab can. We test for flu and COVID on site at our cold and flu service and have results while you wait.
Why same-day care matters for the flu
Antiviral medicines for influenza work best when started within 48 hours of the first symptoms. They can shorten the illness and reduce complications, especially for higher risk patients. That is the strongest reason not to wait out a suspicious fever at home for three days: by the time it is clearly the flu, the treatment window may have closed. Walk in any day we are open.
Go to the ER instead for these
Difficulty breathing, chest pain, confusion, bluish lips, seizures, or signs of dehydration in a child who cannot keep fluids down are emergency room problems. Call 911 or go straight to the ER. For everything else flu related, urgent care is faster and far less expensive; our ER vs. urgent care guide breaks down the difference.
Frequently Asked Questions
When does the 2026-2027 flu season start and peak?
In Southern California, flu activity usually picks up in late fall, peaks between December and February, and can last into spring. Nationally, the CDC reported low but increasing flu activity in late September 2026.
When should I get my flu shot for the 2026-2027 season?
September or October is ideal for most people, so you are protected before flu activity rises. If you miss that window, getting vaccinated later in the season is still worthwhile.
Is the 2026-2027 flu vaccine different from last year's?
Yes. All three virus components were updated for 2026-2027, and every flu vaccine this season is trivalent, protecting against one H1N1, one H3N2, and one B/Victoria virus.
How long does it take for the flu shot to work?
About two weeks. That is why getting vaccinated before flu starts spreading widely matters.
Can I walk in for a flu shot?
Yes. Walk in during business hours, no appointment needed, or save your spot online. We are open Monday to Friday 8:00 AM to 8:00 PM and Saturday and Sunday 9:00 AM to 5:00 PM, and we take our last patient 30 minutes before close.
Who should get a flu shot?
The CDC recommends a yearly flu vaccine for everyone 6 months and older who does not have a reason to avoid it. It matters most for young children, adults 65 and older, pregnant patients, and people with asthma, diabetes, heart disease, or other chronic conditions.
Serving Pasadena, Altadena, Alhambra, Arcadia, and neighboring communities at 797 S Arroyo Pkwy, with free parking and no appointment needed. Call (626) 304-0404.